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Thread: Trailer Build

  1. #1
    smidsy is offline 21 with 19 years experience
    Join Date
    May 2004
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    Sunshine Coast Queensland
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    53
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    Default Trailer Build

    Hei Guys,
    Been planning a trailer, I had to leave mine in WA and they are just too handy to be without.
    My plan is a single axle unbraked 8x5 flat top trailer - in my orginal post I was going to make it wider than my car but I figure a standard size is better and I will make some brackets for flags for reversing visibility.

    My plan is to use 50x50x2 RHS for the frame, 4 beams running front to back and 4 across, plus a front panel about 600mm vertical and the draw bar 1500 from the tray to the towbar. Parts wise I am looking 6 leaf 1500kg springs, 39mm round axle (I would prefer bigger but thats all Active have in the width I want) and ford hubs & rims.
    Long term I would look at removable sides that can be stored underneath but for now I just want it built. I also want double safety chains (the regs say single) and a spare wheel mount.
    Active seem to have all the parts.

    Some questions.
    Floor, I don't really want checker plate, I'm thinking 1.6-2mm sheet will do?
    Secondly, the tray will be high with the wheels underneath, and I want the trailer level when towed with my Falcon. Can I step the draw bar down with additional 50x50 beams - I figure cut the drawbar about 45 degrees on the vertical and weld beams underneath with about a 200mm overlap.

    Lastly, is 50x50x2 too much or not enough, my last trailer had a frame of what looked like about 30x30x3 angle and that lasted 25 years before I sold it. I haven't built a trailer before, but I have pretty good all round skills so I'm confident about the build.

    Thoughts and opinions please.

  2. #2
    Yonnee's Avatar
    Yonnee is offline Trailer Bloke & Mild Mannered Moderator
    Join Date
    May 2007
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    Tooradin, Vic.
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    52
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    1,318

    Default Opininos and thoughts...

    • I would strongly recommend against a combination of a 39mm round axle with 1500Kg springs, and that sized load area of trailer. That sized axle is only rated to 750Kg, including the tare weight of the trailer, and when overloaded, the stiffness of those springs will cause the axle to fail. Springs matched to the axle rating will at least give the axle more of a fighting chance when loaded beyond 750Kg.
    • A standard 6x4 trailer is only as wide as a Falcon, and is 5' 6" to the outside of the guards. so an 8x5'6" flat top tray would be a size that would utilise standard 4' width trailer measurements for the chassis.
    • Additionally, an extra 3" per side would not be a big pain, so to even go out to 8x6 for the top, allowing you to use two 6x4 sheets for the top, and you could still build the chassis to a 4' width. (Just saw your other thread. 6' wide is still 30mm narrower than your Falcon...)
    • With that sized load area, and potential carrying capacity (regardless of axle size), 50 x 50 x 2 is too light for the drawbar. Minimum 75 x 50 x 3.
    • Stepping the drawbar, as you've described, is not usually a problem, but in this case I can suggest that it may not be required. If you build the trailer as two separate parts, the drawbar will be standard height. Firstly, a chassis consisting of Drawbar, two side rails and three cross rails (front, centre and rear) with suspension and axles underneath, just as any ordinary trailer that would be the correct height for the tow vehicle. The Second part being the tray top consisting of the perimeter frame, and cross rails to support the sheet (minimum 600mm apart, recommend 400mm. Either way, this will put a cross rail in the middle should you decide to join two sheets accross as in the third point above). Separating the two halves would be uprights and diagonal bracing. (The gap between the chassis and tray would make great storage area for your removable sides and gates...)
    • Lastly, Active Fab aren't your only option in Brisbane. AL-KO have a branch in Yatala, and can manufacture your axle to spec., as well as having all the other parts.
    Once you decide on trailer width, and your wheel and tyre choice, I can help you with the axle calculation should you wish.

    Hope this has helped for now.

    Yonnee.
    Too many projects, so little time, even less money!
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  3. #3
    Join Date
    Jul 2005
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    Glenroy (Melbourne)
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    Default

    G'day smidsy,
    When deciding on your frame material, keep in mind the change in mass due to various sizes of RHS. It seems like a lot of people get scared about using slightly bigger than 'normal' sections, probably because they're used to commercially made trailers using the absolute minimum amount of steel to protect margins. Makes perfect business sense, but for a trailer you build yourself, why not use much stronger RHS for a 'small' weight penalty?

    I'm not sure what you plan on loading it with, so I won't comment on your internal cross bracing, but you could replace your 7.8 m (2 x 2400 + 2 * 1400) of 50x50x2 frame perimeter with 75x50x3 for an increase in mass of only 19.17 kg. Not much in the grand scheme of things for a substantially stronger trailer.

  4. #4
    smidsy is offline 21 with 19 years experience
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    May 2004
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    Sunshine Coast Queensland
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    Default

    Hei Guys,
    Thanks for the advice.
    What I've decided is to do go with the 75x50x3 for the chassis and 50x50x2 for the tray - to be honest I had planned to build the trailer as one piece but I can see that doing it this way makes sense.
    By my calculations I'm looking at around 130kg for the frame, so hopefully it will come out around the 200kg mark all up.
    I'm also going to match the 1500kg springs with a 1500kg axle and at this stage I'm inclined to go with brakes - the Falcon has a 2.2 ton towing capacity and the rest of the trailer will be 1.5 ton spec so I might as well make it legal. This will just be a general duties trailer but it will be used on country roads.

    I was hoping to do the build at work but the boss has said no so I shall probably wait until tax time because I'll need to buy a welder.

    Cheers

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